446 



ZOOLOGY 



SECT.. 



On its ventral wall is a small, hard, rod-like body, the clitoris (c. c.),, 

 corresponding to the penis of the male, and composed of two- 

 very short corpora cavernosa attached anteriorly to the ischia, with 

 a terminal soft conical glans clitoridis (g. c/.). The vulva, or external 

 opening of the vestibule, is bounded laterally by two prominent 

 folds the Idbia majora. 



Development.- -The Rabbit is viviparous. The ovum, which 

 is of relatively small size, after it has escaped from its Graafian, 

 follicle, passes into the oviduct, where it becomes fertilised,, 

 and reaches the uterus, in which it develops into the fatus r 

 as the intra-uterine embryo is termed. The young animal 



escapes from the uterus in 



"*' a condition in which all 



the parts have become 

 fully formed, except that 

 the eyelids are still closed, 

 and the hairy covering is 

 not yet completed. As 

 many as eight or ten young 

 are produced at a birth,, 

 and the period of gesta- 

 tion, i.e., the time elapsing 

 between the fertilisation 

 of the ovum and the birth 

 of the young animal, is 

 thirty days. Fresh broods 

 may be born once a month 

 throughout a considerable 

 part of the year, and, as 

 the young Rabbit may 

 begin breeding at the age- 

 of three months, the rate 

 of increase is very rapid. 



The segmentation is of 

 the holoblastic type. Am 

 amnion and an allantois. 



are developed much as in the case of the Bird (p. 412). But the- 

 later history of these foetal membranes is widely different in the 

 Rabbit, owing to the modifications which they undergo, in order- 

 to take part in the formation of the placenta the structure by 

 whose instrumentality the foetus receives its nourishment from 

 the walls of the uterus. The placenta is formed from the serous 

 membrane, or outer layer of the amniotic fold, in a limited disc- 

 shaped area, in which the distal portion of the allantois coalesces 

 with it. The membrane thus formed (chorion) develops vascular 

 processes the chorionic mlli which are received into depressions 

 (the uterine crypts) in the mucous membrane of the uterus. The' 



Fio. 1036. Diagrammatic longitudinal section of a 

 Rabbit's embryo at an advanced stage of pregnancy. 

 . amnion ; a, urachus ; at. allantois with blood- 

 vessels , <ls, cavity of yolk-sac ; e. embryo ; cd. endo- 

 dermal layer of yolk-sac ; cd'. inner portion of endo- 

 derrn ; cd". outer portion of endoderm lining the com- 

 pressed cavity of the yolk-sac ; fd. vascular layer of 

 yolk-sac ; pi. placenta! villi ; r. space filled with fluid 

 between the amnion, the allantois and the yolk- 

 sac ; sh, subzonal membrane; st. sinus terminalis. 

 (From Balfour, after Bischoff.) 



